Why is Saturday stronger than Monday?

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

You have 10 balls with you. A friend of yours out of nowhere asks you to place those ten balls in five lines such that each of the lines has exactly 4 balls on them. He needs to check your intelligence. Prove him by doing the task.

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?

What makes this number unique: 8,549,176,320?

If,
29 - 1 = 30
9 - 1 = 10
14 - 1 = 15

Based on similar logic, Can you prove that the below algebraic equation is true?
11 - 1 = 10 ?

An artist while painting a scenic beauty, decides to paint three layers of blue colour on the sky.

Which layer will go on the first?

Which word is least like the others? Third, fourth, fifth, sixth, seventh, eighth, ninth?

There is a place where if I stand up straight, I will still be considered sideways.

A finger goes in me. You fiddle with me when you're bored. The best man always has me first. What am I?